DESCRIPTION: Dr. Matsudaira proposes to continue studies of the Limulus acrosome by: (1) solving the structure of the acrosomal filament and actin bundle and describing calcium-calmodulin-dependent changes in the conformation of actin and scruin; (2) identifying the binding sites involved in scruin-actin, scruin-calmodulin, and scruin-scruin interactions; and (3) measuring the energy stored in the true and false discharge and estimate the energy dissipated during the acrosome reaction.